1. Field of the invention
This invention relates to a metal mold for forming a resin package of a transparent-resin-sealed semiconductor element such as a laser diode and a method for forming the resin package thereof.
2. Description of the Prior Art
FIG. 3 shows the aforementioned laser diode. In FIG. 3, reference numeral 1 designates a semiconductor laser element; 2, a lead frame on which the semiconductor laser element 1 is mounted; and 3, a transparent resin package. The resin package 3 is in the form of a rectangular parallelepiped. The resin package 3 has a light transmitting window 3a in the front end face, which is perpendicular to the optical axis of a laser beam 4 emitted forwardly from the semiconductor laser element 1. It is essential that the light transmitting window is accurately perpendicular to the optical axis of the laser beam, and has a flat molding mirror surface; otherwise, the laser beam from the semiconductor laser element 1 is refracted, so that the emergent light path is bent or the beam is scattered.
FIG. 4 shows the conventional structure of a transfer molding metal mold for forming the resin package. In FIG. 4, reference numeral 5 designates a stationary upper die; 6, a movable lower die; 7, a runner; 8, a gate; and 9 and 10, knock-out pins. Each of the upper and lower dies 5 and 6 is a sectional die; that is, the upper die 5 comprises cavity blocks 5a, 5b and 5c, and the lower die 6 comprises cavity blocks 6a, 6b and 6c. Those cavity blocks are combined to form a cavity.
The resin package 3 is formed with the metal mold as follows: The assembly of the semiconductor laser element 1 and the lead frame 2 is inserted into the metal mold with the lead frame 2 held between the upper die 5 and the lower die 6. Under this condition, transparent casting resin is injected into the metal mold through the runner 7 and the gate 8. Thus the semiconductor laser element with the lead frame has been molded with the resin. Next, while the metal mold being opened, the knock-out pin 9 is operated to release the molding from the upper die 5. Under this condition, the molding still remains in the lower die. Therefore, the knock-out pin 10 is operated to take the molding out of the lower die 6.
The conventional metal mold constructed as described above is disadvantageous in the following points: That is, in the mold shown in FIG. 4, the cavity surface of the cavity block 5a, which surface corresponds to the light transmitting window 3a of the resin package 3, is in parallel with the direction in which the molding is knocked out. Hence, while the molding is being removed from the upper die 5 with the knock-out pin 9, the surface of the light transmitting window 3a of the resin package 3 is rubbed by the cavity surface 5d of the cavity block 5a of the upper die 5, so that the surface of the light transmitting window 3a, which was a molding mirror surface when formed, is scratched, that is, fine scratches are formed in the surface.
The scratched surface is processed as follows: That is, heretofore after the molding is taken out of the metal mold, the scratched surface of the light transmitting window 3a is manually finished into a molding mirror surface by lapping. The lapping operation takes much time and labor, increasing the number of manufacturing steps, and accordingly the manufacturing cost of the semiconductor laser device.